Uplink Power Control for Power Limited Terminals

ABSTRACT

Transmit power control methods and apparatus are disclosed. In several embodiments, a mobile terminal is configured to effectively ignore “UP” transmit power control commands in the event that the mobile terminal is operating in a power-limited state. In an exemplary method for controlling transmit power at a mobile terminal, a plurality of transmit power control commands are received. An accumulated power control value is adjusted in response to each transmit power control command that directs a negative adjustment in transmit power. However, the accumulated power control value is adjusted in response to a transmit power control command that directs a positive adjustment in transmit power only if the mobile terminal is not in a power-limited state. Transmit power settings for each transmission are calculated based on the accumulated power control value and the one or more radio link parameters.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/154,882, filed 9 Oct. 2018, which is a continuation of U.S.application Ser. No. 15/090,734, filed 5 Apr. 2016, now U.S. Pat. No.10,104,623, which is a continuation of U.S. application Ser. No.14/106,094, filed 13 Dec. 2013, now U.S. Pat. No. 9,313,751, which is acontinuation of U.S. application Ser. No. 12/811,736, filed 6 Jul. 2010,now U.S. Pat. No. 8,644,874, which was the National Stage ofInternational Application No. PCT/SE2008/050869, filed 14 Jul. 2008,which claims the benefit of both U.S. Provisional Application No.61/019,337, filed 7 Jan. 2008 and U.S. Provisional Application No.61/019,335, filed 7 Jan. 2008. The disclosures of each of theseapplications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsystems, and in particular relates to methods, apparatus, and systemsfor managing transmission power in a wireless communication system.

BACKGROUND

Radio access technologies for cellular mobile networks are continuouslyevolving to meet demands for higher data rates, improved coverage, andincreased capacity. An example of recent evolution of WidebandCode-Division Multiple Access (WCDMA) technology is the so-calledHigh-Speed Packet Access (HSPA) developed by the 3rd-GenerationPartnership Project (3GPP). Further evolution of 3G systems is ongoingin 3GPP's Long Term Evolution (LTE) initiative, which includes thedevelopment and specification of new access technologies and new systemarchitectures. An overview of the LTE system is provided in “EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Network (E-UTRAN); Overall Description, Stage2, (Release 8)”, 3GPP TS 36.300, v. 8.2.0, September 2007, the contentsof which are incorporated by reference herein.

One goal of the LTE initiative is that the access technology should bedesigned for flexibility, so that it may be used in existing frequencyallocations as well as in new frequency allocations. This approachallows for easy introduction in spectrum with existing deployments. Forsimilar reasons, LTE is designed for use with multiple duplexingsolutions. Both FDD (Frequency Division Duplex) and TDD (Time DivisionDuplex), where uplink and downlink transmissions are separated infrequency and in time respectively, are supported, to permit usage ofLTE technology with paired and unpaired spectrum allocations.Furthermore, to allow for even more flexibility in using availablespectrum, LTE's access technology is based on OFDMA (OrthogonalFrequency Division Multiple Access) for the downlink and Single-CarrierFrequency Division Multiple Access (SC-FDMA) for the uplink. Thesetechnologies permit finely-grained, dynamic allocation of spectrumresources to uplink and downlink communications. Thus, availableresources may be dynamically adjusted based on individual userrequirements as well as aggregate demand.

In wireless communication systems in general, transmitting at excessivepower levels (e.g., at power levels greater than necessary to maintain adesired quality of service) should be avoided. This is generallydesirable to avoid interference with other transmitted signals, and isespecially desirable in a mobile terminal to maximize the time betweenrecharges for the terminal's battery. The LTE specifications thussupport a power control mechanism wherein a serving base station (anevolved Node-B, or eNodeB, in 3GPP terminology) controls a mobileterminal's transmitter output power.

The basic contours of a power control mechanism for LTE are provided in“Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layerprocedures,” 3GPP TS 36.213, v. 8.1.0, dated Dec. 12, 2007, the contentsof which are incorporated herein by reference. The defined mechanismprovides that the power setting for each mobile terminal sub-frametransmission is calculated as a function of the bandwidth allocated forthe sub-frame, the modulation and coding scheme allocated for thesub-frame, and a current path loss estimate. In some operating modes,the transmitter output power is further calculated as a function of aparameter representing accumulated transmit power control (TPC) commandsreceived by the mobile terminal.

This preliminary power control mechanism specified by 3GPP is designedto address the dynamic scheduling allowed in an LTE system. Thebandwidth and modulation scheme employed by the mobile terminal maychange from one sub-frame to the next—to avoid transmitting at excessivepower levels, the transmitter output power level must vary with thesechanges in resource allocations. The transmitter output power level isalso dynamically adjusted to accommodate changes in propagation changes,e.g., transmission path loss. However, the power control mechanismdescribed in the above-mentioned 3GPP specification does not handlepower-limited situations adequately.

Problems with transmit power control mechanisms in power-limitedsituations have been recognized in other wireless communication systems.For instance, U.S. Patent Publication No. 2006/0050798, by Odigie etal., dated Mar. 9, 2006, describes the operation of a transmit powercontrol system in power-limited circumstances for a WidebandCode-Division Multiple Access (W-CDMA) system. However, the methods andapparatus disclosed by Odigie do not address the dynamic resourcescheduling permitted in LTE systems. Furthermore, the systems disclosedin Odigie do not use an accumulated TPC command parameter as required bythe LTE specifications.

SUMMARY

The present disclosure provides methods for efficiently controlling amobile terminal's uplink transmit power in LTE and other systemsutilizing closed-loop power control. In several embodiments, a mobileterminal is configured to effectively ignore “UP” transmit power controlcommands in the event that the mobile terminal is operating in apower-limited state.

In an exemplary method for controlling transmit power at a mobileterminal, a plurality of transmit power control commands are received,each transmit power control command directing an adjustment in transmitpower relative to a prior transmission by the mobile terminal. Anaccumulated power control value is adjusted in response to each transmitpower control command that directs a negative adjustment in transmitpower, i.e., each “DOWN” power control command. However, the accumulatedpower control value is adjusted in response to an “UP” power controlcommand, i.e., a transmit power control command that directs a positiveadjustment in transmit power, only if the mobile terminal is not in apower-limited state. Thus, in some embodiments, the accumulated powercontrol value is adjusted upwards only if the provisional power settingis less than a transmit power limit for the mobile terminal. Theprovisional power setting is calculated from the accumulated powercontrol value and one or more radio link parameters. The method furthercomprises calculating transmit power settings for each transmission bythe mobile terminal based on the accumulated power control value and theone or more radio link parameters.

By ignoring the “UP” power control commands when in a power-limitedstate, the mobile terminal avoids accumulating power control adjustmentsthat are generated by the serving base station while a mobile terminalis power-limited. This approach facilitates a quicker convergence to theoptimal transmit power setting when the mobile terminal exits thepower-limited state.

In one or more embodiments, the provisional power settings and thetransmit power settings are calculated based on the accumulated powercontrol value as well as radio link parameters, which may include one ormore of a transmission bandwidth, a transmission path loss estimate, anda modulation coding scheme. In some embodiments, the provisional powersetting and the transmit power settings may be further calculated as afunction of one or more offset values provided by the serving basestation. These offset values may include one or both of a cell-specifictransmit power offset and a mobile terminal-specific transmit poweroffset. In still other embodiments, the mobile terminal's state ismonitored for the occurrence of one or more predetermined transmit powercontrol reset criteria; the accumulated power control value is reset toa predetermined value in response to each occurrence.

Mobile terminals configured to implement one or more of the powercontrol methods described herein are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an allocation of bandwidth between multiple users inan LTE system.

FIG. 2 a wireless system, including a mobile terminal according to oneor more embodiments.

FIG. 3 is a logic flow diagram illustrating an exemplary method forcontrolling transmit power at a mobile terminal in a wirelesscommunication system.

FIG. 4 is a logic flow diagram illustrating an exemplary method formonitoring for transmit power control reset criteria.

DETAILED DESCRIPTION

In the description that follows, various aspects of the presentdisclosure are described in relation to the 3GPP's LTE standardizationeffort. Those skilled in the art will appreciate that these techniquesmay be applied to other wireless systems utilizing power control.Similarly, methods and apparatus may be described below in reference toan LTE mobile terminal; those skilled in the art will appreciate thatthe techniques described herein may be readily adapted to mobileterminals configured for use in one or more other wireless communicationsystems. Finally, those skilled in the art will appreciate that the term“mobile terminal,” as used herein, is intended to include any of a widevariety of end-user devices, including in particular any of thosedevices referred to as “User Equipment,” “UE,” or “mobile station” bythe various specifications promulgated by the 3rd-Generation Partnershipor other standards groups. Further, the term “mobile station” includeswireless terminals adapted for machine-to-machine (M2M) applications, aswell as wireless terminals adapted for fixed wireless communications.Those skilled in the art will thus appreciate that the mobile terminalsdiscussed herein may comprise cellular radiotelephones with voicecommunications capability, data communications capabilities, or both;personal digital assistant (PDA) devices including wirelesscommunications capability; conventional laptop and/or palmtop computersor other appliances that include a wireless transceiver; and wirelesstransceiver cards and modules adapted for use in host computing devices,which may or may not be portable. Thus, the following description andaccompanying drawings should be viewed as illustrative of the presentdisclosure, and not limiting.

The LTE specification supports fast scheduling and link adaptation, inthe frequency and time domains, for both uplink and downlinkcommunications. This means that resource assignments in time andfrequency can be adjusted to each user's momentary traffic demand andchannel variations. In the LTE uplink, it is possible to scheduleseveral users simultaneously (i.e., in the same sub-frame) by assigningdifferent frequency segments to different users. However, to maintainthe single carrier structure of SC-FDMA, each user can only receive acontiguous assignment in frequency. In other words, although a user maybe assigned a variable number of resource blocks (an LTE resource blockis defined as 12 contiguous subcarriers, each 15 kHz wide, for asub-frame of 1 millisecond in duration), these resource blocks must becontiguous. FIG. 1 illustrates an exemplary allocation of transmitfrequency resources to three users, where User 1 is assigned aconsiderably larger block of frequency resources than User 2 and User 3.These frequency assignments might change from one sub-frame to another,so that, for example, User 1 is assigned fewer resource blocks in asubsequent sub-frame, or no resource blocks at all.

FIG. 2 provides a simplified view of a wireless communication system,including an exemplary mobile terminal 200, configured in accordancewith one or more embodiments, and a base station 250. Mobile terminal200 includes a radio transceiver 210, which in some embodiments may beconfigured according to the LTE specifications. In this case, servingbase station 250 may comprise an evolved Node B, or eNodeB, configuredaccording to LTE specifications. Radio transceiver 210 may also becompatible with one or more additional wireless communication standards,including wide-area wireless network standards such as Wideband CDMA orGSM, or wireless local area network standards such as one or more of theIEEE 802.11 family of standards. Mobile terminal 200 further includes acontroller 220; the functions of controller 220 may include theprocessing of scheduling grant information and transmit power control(TPC) commands received from the base station, and the determination ofpower output settings for transmissions by radio transceiver 210 to basestation 250. In particular, as will be described in more detail below,controller 220 may be configured in some embodiments to adjust anaccumulated power control value in response to each TPC command thatdirects a negative adjustment in transmit power, i.e., “DOWN” TPCcommands, but to adjust the accumulated power control value in responseto each TPC command that directs a positive adjustment in transmit power(“UP” TPC commands) only if a provisional power setting calculated fromone or more radio link parameters and the unadjusted accumulated powercontrol value indicates that the mobile terminal is not power limited.Controller 220 is further configured to calculate transmit powersettings for each transmission by radio transceiver 210 based on theaccumulated power control value and the one or more radio linkparameters.

Mobile terminal 200 also includes memory 230, which may contain softwareand program data for configuring controller 220 according to one or moreembodiments. Memory 230 may also store one or more of the radio linkparameters used by controller 220 in determining power outputsettings—some of these power control parameters may be staticallyconfigured, i.e., stored in memory 230 at time of manufacture, whileothers may be semi-statically configured, i.e., configured by signalinginformation received from base station 250. Memory 230 may further beused for storing the accumulated power control value according to one ormore embodiments. Memory 230 may comprise one or more memory devices,including but not limited to, Flash memory, ROM, RAM (e.g., SRAM and/orDRAM), one or more disk drives, or other volatile or non-volatile memorydevices.

As noted above, a basic power control mechanism for LTE is defined in“Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layerprocedures,” 3GPP TS 36.213, v. 8.1.0, dated Dec. 12, 2007. The definedpower control procedure provides that the power setting for each mobileterminal sub-frame transmission is calculated as a function of thebandwidth allocated for the sub-frame, the modulation and coding schemeallocated for the sub-frame, and a current path loss estimate. In someoperating modes, the transmitter output power is further calculated as afunction of a parameter representing accumulated transmit power control(TPC) commands received by the mobile terminal. If the calculatedtransmitter output power setting exceeds a maximum output power for themobile terminal, then the mobile terminal transmits at the maximumlevel. Thus, a transmit power setting for transmissions on the LTEphysical uplink shared channel (PUSCH) is calculated as:

P _(T)(i)=min{P _(MAX),10·log(BW[i])+Δ_(MCS)(MCS[i])+α·PL+P _(OFFSET)+TPC _(accum)}  (1)

where P_(T)(i) is the power setting for sub-frame i, in dBm, P_(MAX) isthe maximum output power allowed for the mobile terminal, BW[i] is theallocated bandwidth for sub-frame i, in terms of LTE resource blocks (anLTE resource block is 180 kHz wide), Δ_(MCS)(MCS[i]) is a table entryproviding a power level offset for a given modulation/coding schemeMCS[i], PL is a downlink path loss estimate, α is a cell-specificparameter provided to the mobile terminal via higher-layer signaling,P_(OFFSET) is an offset parameter calculated from a cell-specific offsetparameter and a mobile terminal-specific parameter signaled from theeNodeB, and TPC_(accum) is an accumulated power control valuerepresenting an accumulation of transmit power commands received fromthe serving eNodeB. A similar formula is used to compute a transmitpower setting for transmissions on the physical uplink control channel(PUCCH).

The accumulated power control value TPC_(accum) is maintained over timeby updating it based on newly received TPC commands. These TPC commandsare received over a downlink control channel in one of at least twoformats. In the first format, a TPC command is received in a schedulinggrant from the eNodeB. In this format, the TPC command may take onvalues of either [−1,0,1,3] dB, or [−3,−1,1,3] dB, depending onsemi-static configuration parameters determined by higher layersignaling. In a second format, a TPC command for the mobile terminal isjointly coded with other transmit power control commands on the downlinkcontrol channel, and may assume values according to one of the followingsets, again according to semi-static configuration parameters determinedby higher layer signaling: [−1,1] dB, [−1,0,1,3] dB, or [−3,−1,1,3] dB.The accumulated power control value for a given sub-frame i is given by:

f(i)=f(i−1)+Δ_(TPC)(i−4),  (2)

where f(0)=0, and Δ_(TPC)(i−4) represents the value of the TPC commandreceived four sub-frames earlier.

As seen in Equation (1), a mobile transmitter may be power-limited in agiven sub-frame. According to Equation (1), if the power settingcomputed according to the bandwidth, modulation coding scheme, etc.exceeds the maximum power allowed for the mobile terminal, then themaximum power level for the terminal is used. However, the accumulationof TPC commands defined above does not provide an exception forpower-limited cases. As a result, the power control commands areaccumulated even when the mobile terminal is power limited.

For example, when a mobile terminal is allocated a large bandwidth,i.e., when BW[i] in the above formulation is large, and/or when thetransmission path loss PL is large, the power control component10·log(BW[i])+Δ_(MCS)(MCS[i])+α·PL+P_(OFFSET)+TPC_(accum) could belarger than the maximum transmit power. Thus, the mobile terminal ispower-limited. The eNodeB may determine that the mobile terminal has notreached a targeted signal-to-noise ratio (SNR) orsignal-to-interference-plus-noise ratio (SINR) and will thus instructthe mobile terminal to increase power by transmitting “UP” TPC commands,i.e., Δ_(TPC)(i−4)>0. If the power limitation situation lasts for a longtime, the accumulated power control value may continue to grow withoutlimitation. For as long as the mobile terminal is scheduled to transmitwith a large bandwidth, or for as long as the path loss remains high,the mobile terminal may in fact need the maximum transmit power level.(In some scenarios, the transmit power may not be limited to such anextent that the eNodeB completely fails to receive the mobile terminal'stransmissions). However, if the scheduler changes the bandwidthallocation to a smaller bandwidth, or if the radio propagationconditions change significantly, then the mobile terminal's maximumpower might be too large, and the received SINR will exceed the target.Although the open-loop component of the power control formula willadjust to the new bandwidth allocation through the 10·log₁₀(BW[i])component, the accumulated “UP” commands in the closed-loop component(i.e., TPC_(accum)) may cause a problem. If the accumulated powercontrol value TPC_(accum) is large, then the mobile terminal willcontinue to transmit at maximum power until the accumulated powercontrol value is reduced through successive “DOWN” TPC commands. Thismight take several sub-frames; during that time the mobile terminal willtransmit at unnecessarily high power levels, causing interference toother mobile terminal transmitter signals and unnecessarily draining themobile terminal's battery.

One approach to resolving this problem would be to modify the eNodeB'spower control processes. For example, the eNodeB could be configured tostop transmitting “UP” commands if the SINR does not increase inresponse to prior “UP” commands. Alternatively, the eNodeB could beconfigured to avoid transmitting “UP” commands when the bandwidthallocation is large. However, neither of these approaches is likely toresult in optimal performance, because the SINR target will vary due tointerference variations and the frequency selectivity of the channel.This is especially for narrow band allocations. Alternatively, theeNodeB could require the mobile terminal to transmit power reportsfrequently, so that the eNodeB can determine whether the mobile terminalis power limited or not. However, this approach causes considerablesignaling overhead in the uplink.

An improved approach, according to one or more embodiments, is to modifythe power control procedures previously specified by the LTE initiativefor the mobile terminal. In this modified procedure, for operationalmodes in which the transmit power setting is based on an accumulatedpower control value, a provisional power setting is first calculated,using the basic formulation of Equation (1). This provisional powersetting is calculated based on current values for each of the severalradio link parameters. However, the provisional power setting iscalculated based on the previous value for the accumulated power controlvalue. Thus:

P _(PROV)(i)=10·log(BW[i])+Δ_(MCS)(MCS[i])+α·PL+P _(OFFSET) +TPC_(accum)(i−1).  (3)

Updating of the accumulated power control value TPC_(accum)(i−1) isbased on the calculated provisional power setting. In short, positiveTPC commands, i.e. “UP commands” are not accumulated if the mobileterminal is already limited to its maximum output power. That is, ifP_(PROV)>P_(MAX), then TPC_(accum)(i)=TPC_(accum)(i−1)+min{0,Δ_(TPC)(i−4)}. Otherwise, the accumulated power control value is updatedwith any received TPC command. That is, if P_(PROV)≤P_(MAX), thenTPC_(accum)(i)=TPC_(accum)(i−1)+Δ_(TPC)(i−4).

The preceding power control procedure is directly applicable to thedetermination of transmit power settings for transmissions by an LTEmobile terminal, such as mobile terminal 200, on the physical uplinkshared channel (PUSCH). Of course, similar modifications may be made tothe determination of transmit power settings for transmissions on theLTE physical uplink control channel (PUCCH). Of course, those skilled inthe art will appreciate that the techniques described herein may beapplied in other wireless systems, and may be modified in various ways.Thus, a more general overview of a method for controlling transmit powerat a mobile terminal in a wireless communication system is provided inthe flow diagram of FIG. 3.

Each iteration of the logic flow of FIG. 3 begins with the receipt of atransmit power control (TPC) command from a serving base station, asshown at 310. In the LTE system described above, the TPC command couldtake on any of several values, depending on the current configuration ofthe mobile terminal. In some systems, the TPC commands may be limited to“UP” and “DOWN” commands, where “UP” and “DOWN” indicate a fixedincremental adjustment, such as 1 dB, to the previous transmissionpower. In others, the TPC commands may take on a wider range of values.Those skilled in the art will further note that there may be a slightdelay in some systems between actual receipt of the TPC command and itsuse in calculating transmit power settings. For instance, in theLTE-based procedures discussed above, the transmit power settingcalculation for sub-frame i is based on a TPC command received onsub-frame i−4. In other systems, the delay may be longer or shorter thanthis.

As discussed above with regards to LTE, the TPC commands may be receivedfrom the serving base station via a control channel. In someembodiments, the TPC commands may be transmitted according to ascheduling assignment format or a power control command format; thus,some embodiments may be required to extract the transmit power controlcommands from the control channel according to either or both of theseformats.

In any event, if the TPC command indicates a downward adjustment, i.e.,if the directed adjustment to the previous transmit power is negative,as determined at block 320, then processing continues at block 350,where an accumulated power control value is adjusted according to theTPC command. At block 360, the transmit power setting for a currenttransmission is then calculated, based on the accumulated power controlvalue and one or more radio link parameters. In the LTE setting, theseradio link parameters include a transmission bandwidth allocation,modulation/coding scheme parameters, and a transmission path lossestimate. In other systems the radio link parameters may include one ormore of these radio link parameters and/or one or more other radio linkparameters. In some embodiments, the calculation at block 360 of thetransmit power setting may also be based on one or more offset values.These offset values might include a cell-specific transmit power offsetor a mobile terminal-specific transmit power offset, or both. One ormore of these offset values may be received from the serving basestation.

Those skilled in the art will appreciate that the transmit power settingcalculated in block 360 may in some circumstances reflect apower-limited situation even if the accumulated power control value hasjust been adjusted downwards. However, each downward adjustment of theaccumulated power control value makes the mobile terminal somewhat“less” power-limited than it would otherwise have been. After severalsuch adjustments to the accumulated power control value, the mobileterminal may leave the power-limited state, so that subsequent TPCcommands actually cause a downward adjustment in transmit power.

On the other hand, if the received TPC command indicates an upwardadjustment relative to the previous transmit power, again as determinedat block 320, then a provisional power setting is calculated at block330. The provisional power setting is calculated based on the same oneor more radio link parameters discussed above, but is based on a priorsetting for the accumulated TPC value, e.g., the immediately previousvalue. Thus, the provisional power setting calculation reflects atransmit power setting assuming that the accumulated TPC value is notadjusted upward according to the current TPC command. Of course, theprovisional power setting is not necessarily calculated “fromscratch”—in some cases, the provisional power setting may be calculatedby simply adjusting a previous provisional power setting for any changesin the radio link parameters.

At block 340, the mobile terminal determines whether it ispower-limited, based on the provisional power setting. In someembodiments, the mobile terminal is determined to be power-limited ifthe provisional power setting is greater than the power limit for themobile terminal. In others, the mobile terminal is deemed power-limitedif the provisional power setting is greater than or equal to the mobileterminal's power limit. In either case, if the mobile terminal ispower-limited, then the accumulated power control value is not adjusted,and processing passes to block 360, where the transmit power setting iscalculated. In this event, of course, the transmit power setting will bethe maximum permitted for the mobile terminal, since the mobile terminalis power-limited.

If, on the other hand, the provisional power setting is less than themobile terminal's power limit, then the accumulated power control valueis adjusted, at block 350, to reflect the received “UP” TPC command. Thetransmit power setting is calculated at block 360; the transmit powersetting in this case reflects the current radio link parameters and theupdated accumulated power control value.

In the method pictured in FIG. 3, it is implicitly assumed that a prioraccumulated power control value exists; i.e., that a previous value forthe accumulated power control value can be updated based on a receivedTPC command. In the LTE specification referenced earlier, theaccumulated transmit power command value is initialized to zero;however, no criteria for resetting the accumulated power control valuesare defined. In practice, various criteria for resetting the accumulatedpower control values may be needed. For example, as those skilled in theart will appreciate, different cells may have different uplink/downlinkpath loss mismatches due to feeder losses and other deployment-relatedaspects. When a mobile terminal enters a new cell, any cell-specificoffset values used in the calculation of the transmit power settings maybe updated to reflect the new cell configuration. This may be done, forinstance, by receiving new cell-specific offset values transmitted tothe mobile station via the control channel. These new cell-specificoffset values may then be used by the mobile terminal in subsequentpower setting calculations. However, if the accumulated power controlvalues is not reset in such a situation, adjustment of the transmitpower settings to an appropriate level could be unnecessarily delayed.Indeed, since TPC commands in LTE are typically only transmitted when amobile terminal has data for transmission, and not in advance, this mayresult in unnecessary hybrid automatic repeat request (HARQ)retransmissions and HARQ failures. Furthermore, if the new cell isunaware of the TPC commands sent from the first cell, the new eNodeBcannot track the mobile terminal's transmit power. There may be othersituations where resetting the accumulated TPC values is advantageous,such as when a UE attempts uplink synchronization after uplinksynchronization loss.

Accordingly, in some embodiments, a mobile terminal is provided withcriteria for when to restart the accumulation of the TPC. For instance,an LTE mobile terminal may be configured with criteria for resetting TPCaccumulation corresponding to uplink transmissions on the shared uplinkchannel (PUSCH). In some embodiments, the same criteria may be used toreset a separate accumulation of the uplink control channel (PUCCH) TPCcommands. In others, separate criteria may be provided for resetting theaccumulated TPC value for the PUCCH.

Examples of such criteria include, but are not limited to: detection ofa change in serving cell; an attempt to acquire uplink synchronizationafter synchronization loss; a long discontinuous receive mode DRXperiods—e.g., if the time since a transmission on the PUSCH or PUCCHexceeds a configured threshold; the entering or leaving of active state;receipt of a TPC command indicating that an absolute power offset,rather than an accumulated power control value, should be used incalculating the transmit power setting; and a change in one or more ofsystem-controlled power control parameters, such as the path lossscaling factor α or the offset parameter P_(OFFSET) of Equation (1).Those skilled in the art will appreciate that various criteria may alsobe formed by combining two or more of the above criteria (or othercriteria) using logical “AND” and/or “OR” operations.

FIG. 4 thus illustrates a method for evaluating whether the accumulatedpower control value should be reset. In some embodiments, theaccumulated power control value is reset to zero, although otherinitialization values are possible. Those skilled in the art willappreciate that the method illustrated in FIG. 4, or variants thereof,may be combined, in some embodiments, with the method illustrated inFIG. 3.

In any case, each iteration of the method pictured in FIG. 4 begins withan evaluation of whether the serving cell has changed, as shown at block410. (Of course, the pictured evaluations in blocks 410-460 may beperformed in any order.) If so, control passes to block 470, where theaccumulated power control value is reset. If not, then additionalcriteria for resetting the accumulated power control value are evaluatedin a similar fashion. Thus, the mobile station determines whether uplinksynchronization was lost, at block 420, whether the time since a lasttransmission exceeds a predetermined threshold, at block 430, andwhether a new power control parameter was received from the serving basestation, at block 440. Similarly, the mobile station evaluates whetherit has left or entered active state, at block 450, and whether it hasreceived an absolute power offset command from the base station, atblock 460. If any of these reset criteria are met, then the accumulatedpower control value is reset, at block 470. Otherwise, the criteriacontinue to be re-evaluated.

The various methods described above, as well as variations thereof, maybe implemented on mobile terminals, such as the mobile terminal 200pictured in FIG. 2, configured for operation in a wireless communicationsystem employing closed-loop power control. The present disclosure may,of course, be carried out in other ways than those specifically setforth herein without departing from essential characteristics of thepresent disclosure. The present embodiments are thus to be considered inall respects as illustrative and not restrictive, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein.

What is claimed is:
 1. A method for controlling transmit power at a mobile terminal in a wireless communication system, the method comprising: receiving a plurality of transmit power control commands, each transmit power control command directing an adjustment in transmit power relative to a prior transmission by the mobile terminal; adjusting an accumulated power control value in response to a transmit power control command that directs a positive adjustment in transmit power when the mobile terminal is not in a power-limited state; calculating a transmit power setting for a transmission by the mobile terminal based on the accumulated power control value and a transmission bandwidth allocated for the transmission, wherein the transmission bandwidth allocated for transmissions by the mobile terminal is variable per transmission; monitoring for an occurrence of one or more predetermined transmit power control reset criteria, wherein the predetermined transmit power control reset criteria include one or more of: a change in serving cell for the mobile terminal; a loss of uplink synchronization; and elapse of a pre-determined period with no transmissions by the mobile terminal; and resetting the accumulated power control value to a pre-determined value in response to the occurrence.
 2. The method of claim 1 wherein the mobile terminal is in the power-limited state when transmissions by the mobile terminal are performed at a transmission bandwidth and/or radio propagation conditions that require the mobile terminal to transmit at the maximum transmit power.
 3. The method of claim 1 wherein receiving a plurality of transmit power control commands comprises: receiving a control channel from a serving base station; and extracting the transmit power control commands from the control channel.
 4. The method of claim 3 wherein extracting the transmit power control commands from the control channel comprises extracting the transmit power control commands according to a scheduling assignment format or a power control command format.
 5. The method of claim 1 wherein calculating the transmit power setting for the transmission by the mobile terminal based on the accumulated power control value and the transmission bandwidth allocated for the transmission further comprises calculating the transmit power setting as a function of at least one of a transmission path loss estimate and a modulation and coding scheme.
 6. The method of claim 1 further comprising receiving one or more offset values from a serving base station, and wherein calculating the transmit power setting for the transmission by the mobile terminal further comprises calculating the transmit power setting based on the one or more offset values.
 7. The method of claim 6 wherein the one or more offset values include one or both of a cell-specific transmit power offset and a mobile terminal specific transmit power offset.
 8. The method of claim 1 wherein the predetermined transmit power control reset criteria further include: receipt of a changed power control parameter from the serving cell.
 9. A mobile terminal configured for use in a wireless communication network, the mobile terminal comprising: a radio transceiver; and a control circuit configured to: receive a plurality of transmit power control commands, each transmit power control command directing an adjustment in transmit power relative to a prior transmission by the mobile terminal; adjust an accumulated power control value in response to a transmit power control command that directs a positive adjustment in transmit power when the mobile terminal is not in a power-limited state; calculate a transmit power setting for a transmission by the mobile terminal based on the accumulated power control value and a transmission bandwidth allocated for the transmission, wherein the transmission bandwidth allocated for transmissions by the mobile terminal is variable per transmission; monitor for an occurrence of one or more predetermined transmit power control reset criteria, wherein the predetermined transmit power control reset criteria include one or more of: a change in serving cell for the mobile terminal; a loss of uplink synchronization; and elapse of a pre-determined period with no transmissions by the mobile terminal; and reset the accumulated power control value to a pre-determined value in response to the occurrence.
 10. The mobile terminal of claim 9 wherein the mobile terminal is in the power-limited state when transmissions by the mobile terminal are performed at a transmission bandwidth and/or radio propagation conditions that require the mobile terminal to transmit at the maximum transmit power.
 11. The mobile terminal of claim 9 wherein the radio transceiver is further configured to: receive a control channel from a serving base station; and extract the transmit power control commands from the control channel.
 12. The mobile terminal of claim 11 wherein the radio transceiver is further configured to extract the transmit power control commands from the control channel according to a scheduling assignment format or a power control command format.
 13. The mobile terminal of claim 9 wherein the control circuit is further configured to calculate the transmit power setting as a function of at least one of a transmission path loss estimate and a modulation and coding scheme.
 14. The mobile terminal of claim 9 wherein the radio transceiver is further configured to receive one or more offset values from a serving base station, and wherein the control circuit is further configured to calculate the transmit power setting based on the one or more offset values.
 15. The mobile terminal of claim 14 wherein the one or more offset values include one or both of a cell-specific transmit power offset and a mobile terminal specific transmit power offset.
 16. The mobile terminal of claim 9 wherein the predetermined transmit power control reset criteria further includes: receipt of a changed power control parameter from the serving cell.
 17. A method for controlling transmit power at a mobile terminal in a wireless communication system, the method comprising: receiving a plurality of transmit power control commands, each transmit power control command directing an adjustment in transmit power relative to a prior transmission by the mobile terminal; adjusting an accumulated power control value in response to a transmit power control command that directs a positive adjustment in transmit power when the mobile terminal is not in a power-limited state; calculating a transmit power setting for a transmission by the mobile terminal based on the accumulated power control value and a transmission bandwidth allocated for the transmission, wherein the transmission bandwidth allocated for transmissions by the mobile terminal is variable per transmission; monitoring for an occurrence of one or more predetermined transmit power control reset criteria, wherein the predetermined transmit power control reset criteria include one or more of: a loss of uplink synchronization; and elapse of a pre-determined period with no transmissions by the mobile terminal; and resetting the accumulated power control value to a pre-determined value in response to the occurrence. 